A combination of increasing energy costs and increased environmental awareness has led to a desire by individuals and businesses to curb energy waste. One particular area of energy waste that has attracted attention is the area of wasted standby power, sometimes known as vampire or phantom power. Most modern appliances no longer completely shut off but, instead, enter into a standby power state. In this state, these appliances wait for an event, such as an infrared remote signal, a time trigger or a push of a button, to return to a full power state. Computer monitors, printers, connection hubs, televisions, amplifiers, DVD players, game consoles and many other common appliances all exhibit this behavior.
Because these appliances spend the majority of their operational life in standby, aggregate power consumption in standby is often significantly greater than the power used when the devices are actually in use. And since such devices are common, estimates suggest that between 10% and 20% of the modern electrical budget is consumed by appliances in standby, waiting to be used. Standby power waste has grown significantly in the last decade and expected to increase into the future as more devices upgrade to using a standby mode to enable them to “turn on” instantly.
Shutting off appliances manually, or unplugging them when not in use, is neither convenient nor practical. In many cases, master power switches are hidden in difficult to access areas and the outlets into which these appliances are plugged are often inaccessible. Furthermore, there may be many such appliances in a single home or office.
The growing popularity of personal computers, particularly laptop computers, has created a significant standby power problem. Appliances used in conjunction with computers and laptops, such as printers, hubs, monitors and speakers, often remain on, perpetually waiting for the laptop to be connected. Even though these appliances are not in use, often for extended periods of time, they continue to consume power.
One prior art solution to this problem is a current sensing automatic shut-off apparatus. One example of a prior art mechanism of this type is a traditional multi-outlet power strip with a combination of a current measuring outlet and one or more controlled outlets. The current measuring outlet is permanently powered and measures the current draw of the attached “measured” appliance, a personal computer or television, for example. The controlled outlet(s) are attached to an automatic electrical disconnection device, which connects to or disconnects from power depending on the amount of current measured at the current measuring outlet. Using such an apparatus, “controlled” appliances, such as amplifiers, printers, hubs and DVD players, can be fully de-powered whenever the measured appliance goes into standby mode and then re-powered when the primary appliance is returns to normal operation mode. Such a mechanism can reduce the amount of standby draw from that of many appliances to that of the single appliance, thereby saving significant energy.
The simplest types of these current-measuring mechanisms use analog circuitry to measure current consumed through the current measuring outlet and use the results of the measurement to trigger the control outlet(s). Specifically, control outlet(s) are powered whenever the current measured at the current measuring outlet exceeds a pre-set threshold. In some instances the threshold is fixed. In others it can be adjusted using a tunable potentiometer. These mechanisms work reasonably well for measured appliances that fit pre-determined criteria. However, these mechanisms can become unstable if the transition of the measured appliance from standby to in-use occurs at a current value at or near the pre-set trigger threshold. In such a scenario, these mechanisms tend to power and de-power the control outlet(s) repeatedly and rapidly, which can damage appliances attached to the control outlet(s).
Another prior art mechanism uses a digital controller to calibrate the trigger threshold in order to avoid the instability problem introduced by a pre-set threshold. In this prior art system, the mechanism measures the maximum current draw during operation of the appliance attached to the current measuring outlet and uses this measurement to determine a trigger threshold. Even using a simple formula, such as percentage of maximum measured current, to calibrate the trigger threshold avoids the problem of malfunction possible with a pre-set threshold. However, the digital prior art system functions on the assumption that the appliance being measured operates in two distinct power modes, a lower current standby mode and a higher current active mode. This assumption is reasonably valid for appliances such as television sets and even some desktop computers. However, many appliances, particularly re-chargeable appliances such as laptop computers, exhibit complex power consumption behavior and will completely confuse such a mechanism.